1. Field of the Invention
The present invention relates to a magnetoresistance magnetic reading head for a perpendicular recording, as well as to a process for producing such a head. The invention is used in reading on a magnetic tape and optionally writing information on a support such as a disk or tape.
2. Discussion of the Background
A known horizontal magnetic reading and writing head for a perpendicular recording on a magnetic tape is shown in FIG. 1. It is possible to see a thick horizontal magnetic layer 2 having a central pole piece 3, a conductor coil 4 surrounding said pole piece and embedded in an insulating layer 5, a thin magnetic monopole 6 extending the central pole piece and finally a hard dielectric layer 7 making it possible to obtain an outer planar surface ("flight plane").
The support on which the information is written and read is constituted by a magnetic layer 10 deposited on a substrate 12. The assembly passes infront of the monopole 6.
The operation of such an apparatus is as follows. The magnetic field created by the flow of a current in the coil 4 has its lines very close together in the monopole 6 and divides and is then closed again by the lateral pole pieces of the thick magnetic layer 2. Under these conditions, the magnetic induction in the recording zone of the layer 10 is perpendicular thereto. This is why such apparatuses are called perpendicular or vertical recording heads. On reading, the variation of the flux detected by the monopole induces a current in the coil. Such a head is recorded in U.S. Pat. No. 4,731,157 granted to J. P. Lazzari on Mar. 15, 1988.
It is also pointed out that another category of reading and writing heads designed for reading or writing a magnetic induction located in the plane of the magnetic layer is known. The heads are called longitudinal or horizontal recording heads. They comprise a magnetic circuit with an air gap. They play no direct part in the present invention.
Independently of the technology of thin film heads, efforts have been made to form magnetic information reading heads using magnetoresistant elements. It is known that a magnetoresistor has magnetization, whose direction can rotate under the effect of an external magnetic field. This rotation is accompanied by a variation .DELTA.R of the resistance R of the layer. This resistance can be measured by passing a weak current into the layer. In practise, for a 0.1 .mu.m thick iron-nickel layer, the resistance variation is approximately 1% when the angle of the magnetization turns by 90.degree.. To increase the sensitivity of the measurement and improve the linearity, it is possible to orient the magnetization of the magnetoresistance layer beforehand to 45.degree. of the current lines.
Such a magnetoresistance apparatus is described in U.S. Pat. No. 4,703,378, the apparatus being placed beneath a space interrupting a magnetic circuit forming an air gap.
In the same way, European Patent 284 495 describes an apparatus with two magnetoresistors positioned to the rear of a magnetic circuit defining an air gap.
In all cases, these are heads for longitudinal recording, i.e. with an air or head gap. No perpendicular recording apparatus equipped with a magnetoresistor is known.